1. Technical Field
The technical field relates to communication devices, and more particularly to communication devices utilizing a data link layer and a point-to-point protocol (PPP).
2. Description of the Related Art
The main application of the PPP and the communication devices operating on that basis is in the field of so-called IP networks. That can be for example the Internet but also a private intranet. Using special surfaces and interfaces, for example RS232, IRDA, Bluetooth or Comport by way of USB, a data stream occurring in those networks is serially transmitted. The packet-oriented PPP protocol has prevailed as the general standard for such serialization. A communication device operating on the basis of the PPP can be for example a modem.
The structure of the PPP known from the state of the art provides that whenever there is a data communication such devices completely occupy the interface which is present in that respect on the hardware side. In that case the communication device is in a state which is referred to as the data mode. Additional commands which are not part of the transmitted data stream cannot be sent to the communication device under those conditions. Sending additional commands however is generally performed when for example the so-called AT commands have to be communicated, which are utlilized for checking and verifying a link quality, for displaying items of network information about field strengths or network operators, for establishing a charge condition of an accumulator, for terminating a connection and the like further monitoring and control functions.
In addition, particularly in the case of communication devices which fulfill a function as a wireless modem, it is of great significance that, besides data transmission, additional services or applications can be implemented. For that purpose access to the hardware of the communication device is made possible for those services in parallel with the ongoing data transmission. That is the case for example with applications which are intended to serve at any time to drop or accept speech calls, send or receive short messages (SMS) and thus to use further functions of the communication device.
For that purpose some solutions are already known from the state of the art: in a first procedure the communication device is set from a data mode into a so-called command mode. In that case the data transmission is interrupted and the communication device is then available in the command mode for the active application. That switching-over operation is generally effected by special sequences of characters or control signals. In those switching-over operations however the flow of data is considerably slowed down by way of the communication device. In addition the time behavior of protocols on higher abstraction layers is adversely affected.
To send commands to the communication device in parallel with the existing data connection therefore additional physical interfaces are used, by way of which on the one hand the data connection and on the other hand transmission of the commands is implemented. Desirably multiplexer protocols are used, with which a plurality of logic channels can be provided on a physical interface at the communication device, by way of which a plurality of applications can send commands to the communication device. Basically however even with those technical solutions the data mode of the communication device is temporarily terminated and thus the existing data connection is then broken off so that the applications and services operating in the command mode can access the communication device.
In addition implementation and integration of the multiplexer protocol is often linked to additional problems. In part considerable development work is involved to produce such a protocol. A multiplexer protocol also places high demands on the processors and memories in the communication device. Often the multiplexer protocol can only be implemented in limited circumstances.